The present invention relates to an apparatus for detecting an air/fuel ratio of engines such as an automotive engine.
Typically, automotive engines include an air/fuel-ratio sensor (including an oxygen sensor) arranged in an exhaust pipe or the like and for detecting the oxygen concentration or the like in exhaust gas.
The air/fuel-ratio sensor comprises typically an elongate plate-like heater, an oxygen-ion conductive solid electrolyte layer formed on the heater in a laminated way and activated by heat therefrom, a plurality of electrodes arranged on the surface of the electrolyte layer, and a gas diffusion layer which cooperates with the electrolyte layer to externally cover the electrodes.
The air/fuel-ratio sensor detects an engine air/fuel ratio by measuring pumping current or diffusion limiting current which passes between the electrodes when externally applying the voltage to the air/fuel-ratio sensor.
Using an air/fuel-ratio detection signal derived from the air-fuel-ratio sensor, an engine electronic control unit feedback-controls a fuel-injection amount in such a way as to bring the air/fuel ratio close to a theoretical value (A/F=14.7), a lean value (A/F≧15), and the like, thereby enhancing the combustion efficiency and fuel consumption of the engine.